The present invention relates to a reversible transmission mechanism which is capable of converting the rotation of an input member to the rotation of an output member in either direction.
It is required that some of a large number of rollers used in copiers and printers be rotatable in either direction in order to e.g. print both sides of sheets. Rotation is transmitted to such rollers through reversible transmission mechanisms, which include two types, i.e. one including spur gears through which rotation is transmitted to the output shaft, and one including bevel gears through which rotation is transmitted to the output shaft. In the former type, because the input and output shafts have to be disposed parallel to each other while being sufficiently spaced from each other, this reversible transmission mechanism is not sufficiently compact. The latter type is not compact either, because the input and output shafts have to be arranged to extend perpendicular to each other.
There are also known reversible transmission mechanisms which can convert the rotation of the input member to the rotation of output member in either direction through bevel gears, with their input and output members mounted on a single common shaft. One such reversible transmission mechanism is disclosed in JP patent publication 4-39126A, which is a steering gear box comprising an input shaft (input member), an output shaft (output member), a first boss (intermediate member) rotatably disposed around the input shaft, bevel gears rotatably mounted on fixed shafts and meshing with the input shaft and the first boss to rotate the first boss in a direction opposite to the direction in which the input shaft is rotated, a second boss fixed to the input shaft and rotated in the same direction as the input shaft, and a sleeve which is axially movable to selectively couple one of the first and second bosses to the output shaft, thereby selectively rotating the output shaft in one of the opposite directions. The sleeve is also movable to a neutral position where the output shaft is coupled to neither of the first and second bosses and thus freely rotatable.
Although the reversible transmission mechanism disclosed in this publication has its input and output members disposed coaxially with each other, since it is necessary to provide the intermediate member around the input member between the input and output members in order to rotate the output member in the reverse direction, extra parts are required to support the intermediate member, in addition to the intermediate member itself. This reversible transmission mechanism is naturally complicated in structure.